This invention pertains to desulfurization of solvent refined coal liquefaction products.
As background to the present invention, U.S. Pat. No. 4,077,866--Owen et al appears to be of primary interest. It proposes a solvent coal refining process in which the coal slurry is desulfurized by contact with a solid sulfur scavenger, such as iron (but which may include any of numerous other materials, some of which are also disclosed herein). The inclusion of the sulfur scavenger in the solvent-coal slurry, in accordance with the process of the Owen et al patent, differs from the present invention in that Owen et al would require sufficient scavenger to react with substantially all of the sulfur present. This includes volatile low molecular weight sulfur compounds and hydrogen sulfide. Indeed, with regard to one example, the Owen et al patent states that (following desulfurization) no gaseous hydrogen sulfide was evolved (Col. 9, lines 55-56).
Other patents considered as background to the present invention include U.S. Pat. Nos. 3,284,345--Ishiko et al; 2,697,064--Brown; 738,656--Burwell et al; 1,587,491--Cross; 3,063,936--Pearce et al; 3,769,197--Leas et al; and 4,190,518--Giannetti.
Ishiko et al teach desulfurization of crude oil or heavy oil by contact with a particularly reactive form of reduced iron powder. A process of this general nature, as related to petroleum fractions, is also referred to in the background portion of the Brown patent.
Other sulfur-reactive reagents are used for desulfurizing vapor phase petroleum products according to the processes disclosed in the Burwell et al and Cross patents.
A more complex desulfurization process for hydrocarbon oils, such as petroleum fractions, but including some of the same sulfur reactants included in the disclosure of the present invention, is seen in U.S. Pat. No. 3,063,936--Pearce et al.
Finally, U.S. Pat. Nos. 3,769,197--Leas et al and 4,190,518--Giannetti et al both pertain to solvent refined coal desulfurization processes, wherein sulfur is extracted by reaction in the vapor phase. Coincidentally, the solvent coal slurry in the Giannetti et al process is hydrogenated (and any sulfur compounds present probably converted to some other form) in the presence of a hydrogenation catalyst, which is chosen from a wide range of materials including many compounds similar to those referred to herein as sulfur getters.
Notwithstanding these prior processes, there remains a continuing need for more efficient means for desulfurizing solvent refined coal products, and particularly the non-volatile portions thereof. Because, non-volatile sulfur compounds in solvent refined coal products tend to be high molecular weight multi-cyclic anthracene and phenanthrene-type compounds, such compounds are somewhat more difficult to remove than other sulfur compounds. In high boiling point solvent refined coal fractions, these heavy sulfur compounds may comprise on the order of 1% by weight of the product. However, reduction of sulfur content in these fractions, by as little as a tenth of a percent, may be significant in some circumstances.
It is therefore the general object of the present invention to provide a solvent coal refining desulfurization process improved with respect to simplicity and efficiency of sulfur capture as compared to prior known processes.